nixos/clan: add option for opting out of Clan defaults

Also replace `documentation.nixos.enable = false` with
`documentation.doc.enable` to opt out of only `nixos-help` and the HTML
manual but leave `man configuration.nix`.

nixosModules/clanCore/default.nix

@@ -1,10 +1,9 @@
-{ lib, config, ... }:
 {
   imports = [
     ./backups.nix
+    ./defaults.nix
     ./facts
     ./inventory
-    ./manual.nix
     ./meta/interface.nix
     ./metadata.nix
     ./networking.nix
@@ -12,7 +11,6 @@
     ./nix-settings.nix
     ./options.nix
     ./outputs.nix
-    ./packages.nix
     ./schema.nix
     ./sops.nix
     ./vars
@@ -22,14 +20,4 @@
     ./zfs.nix
   ];
 
-  # Use systemd during boot as well except:
-  # - systems with raids as this currently require manual configuration: https://github.com/NixOS/nixpkgs/issues/210210
-  # - for containers we currently rely on the `stage-2` init script that sets up our /etc
-  boot.initrd.systemd.enable = lib.mkDefault (!config.boot.swraid.enable && !config.boot.isContainer);
-
-  # Work around for https://github.com/NixOS/nixpkgs/issues/124215
-  documentation.info.enable = lib.mkDefault false;
-
-  # Don't install the /lib/ld-linux.so.2 stub. This saves one instance of nixpkgs.
-  environment.ldso32 = null;
 }

nixosModules/clanCore/defaults.nix

@@ -0,0 +1,42 @@
+{
+  lib,
+  config,
+  pkgs,
+  ...
+}:
+{
+  options.clan.core.setDefaults = (lib.mkEnableOption "Clan defaults") // {
+    default = true;
+    example = false;
+  };
+
+  config = lib.mkIf config.clan.core.setDefaults {
+    # Use systemd during boot as well except:
+    # - systems with raids as this currently require manual configuration: https://github.com/NixOS/nixpkgs/issues/210210
+    # - for containers we currently rely on the `stage-2` init script that sets up our /etc
+    boot.initrd.systemd.enable = lib.mkDefault (!config.boot.swraid.enable && !config.boot.isContainer);
+
+    # This disables the HTML manual and `nixos-help` command but leaves
+    # `man configuration.nix`
+    documentation.doc.enable = lib.mkDefault false;
+
+    # Work around for https://github.com/NixOS/nixpkgs/issues/124215
+    documentation.info.enable = lib.mkDefault false;
+
+    # Don't install the /lib/ld-linux.so.2 stub. This saves one instance of nixpkgs.
+    environment.ldso32 = null;
+
+    environment.systemPackages = [
+      # essential debugging tools for networked services
+      pkgs.dnsutils
+      pkgs.tcpdump
+      pkgs.curl
+      pkgs.jq
+      pkgs.htop
+
+      pkgs.nixos-facter # for `clan machines update-hardware-config --backend nixos-facter`
+
+      pkgs.gitMinimal
+    ];
+  };
+}

nixosModules/clanCore/manual.nix

@@ -1,4 +0,0 @@
-{ pkgs, ... }:
-{
-  documentation.nixos.enable = pkgs.lib.mkDefault false;
-}

nixosModules/clanCore/networking.nix

@@ -91,7 +91,7 @@
       ]
     )
   ];
-  config = {
+  config = lib.mkIf config.clan.core.setDefaults {
     # conflicts with systemd-resolved
     networking.useHostResolvConf = false;
 

nixosModules/clanCore/nix-settings.nix

@@ -1,7 +1,7 @@
-{ lib, ... }:
+{ lib, config, ... }:
 # Taken from:
 # https://github.com/nix-community/srvos/blob/main/nixos/common/nix.nix
-{
+lib.mkIf config.clan.core.setDefaults {
   # Fallback quickly if substituters are not available.
   nix.settings.connect-timeout = 5;
 

nixosModules/clanCore/packages.nix

@@ -1,18 +0,0 @@
-{
-  pkgs,
-  ...
-}:
-{
-  environment.systemPackages = [
-    # essential debugging tools for networked services
-    pkgs.dnsutils
-    pkgs.tcpdump
-    pkgs.curl
-    pkgs.jq
-    pkgs.htop
-
-    pkgs.nixos-facter # for `clan machines update-hardware-config --backend nixos-facter`
-
-    pkgs.gitMinimal
-  ];
-}